On Ajora:
Ajora was born at a time when airships flew across the skies. It was recorded that the day he was born Ajora walked up on two feet and went to a well, pointing out that it was poisoned. True to this, during the Black Death, many who drank from the well died. Those surviving called it his miracle, and Ajora a child of the gods. As he continued to preach, his influence grew.
At the age of 20, Ajora prophesied the coming of Paradise. This was the last straw, and the Pharist priests of the dominant religion at the time reported him to the Holy Ydoran Empire, who named him heretic and traitor. Germonique, one of Ajora's disciples, sold information about his whereabouts, and Ajora was executed at the Golgollada Gallows. His death caused Mullonde to be wiped out in a tidal wave and those who had faith in Ajora created the Church of Glabados.
https://finalfantasy.fandom.com/wiki/Ajora_Glabados
For Kiltia, Vagrant Story covers some of it, so it would be more of a Vagrant Story prequel:
https://finalfantasy.fandom.com/wiki/Kiltia